The present invention relates to an apparatus for detecting the rotation position of a crankshaft of an engine in an automobile or the like, and particularly to an apparatus capable of detecting instantly the rotation position of a rotating body such as a crankshaft under any rotation speed.
There has been proposed apparatus for detecting the revolution of the crankshaft of the engine in automobile, or the like in which a magnetic substance with a coil thereon is used to oppose the rotating body so that an alternating electromotive force can be induced in the coil by the change of magnetic flux due to the unevenness or projections of the rotating body, thereby detecting the revolution of the rotating body.
In this kind of apparatus, however, the alternating electromotive force induced in the coil is affected by the change of magnetic flux threading the coil, or the revolution speed of the rotating body. When the rotating body is at a low speed, the coil induces only a small alternating e.m.f. so that the rotation of the rotating body can not be detected.